1. Field of the Invention
The present invention relates to the structure of ball rolling grooves for a linear guide apparatus, which receives loads through a number of balls infinitely circulating while rolling in the ball rolling grooves formed opposedly on both sides of a guide rail and the slider which travels freely thereon. More particularly, the invention relates to the structure of ball rolling grooves for a linear guide apparatus suited for the use of a guide bearing for the principal part of a machine tool which requires minute and precise operations.
2. Related Background Art
In the linear guide apparatus, there are formed two rows of ball rolling grooves 3 each on either side of the guide rail 1 extending in the axial direction as shown in FIG. 4 to FIG. 6, and a ball rolling groove 5 facing the aforesaid ball rolling groove 3 and a ball returning pass 7 in parallel thereto are provided each on both sleeves of the slider 2 which is slidably mounted on the guide rail 1. Thus, a number of balls B rolling in both of the ball rolling grooves 3 and 5 following the traveling of the slider 2 are guided into the ball returning pass 7 so that the balls are infinitely circulated. In the case of the conventional linear guide apparatus, the structure of the ball rolling grooves is confined either to a four-point contact type or a two-point contact type.
In other words, the structure shown in FIG. 4 is of a four-point contact type, in which the groove surfaces of both opposed ball rolling grooves 3 and 5 and the balls B are in contact at four points in each of the upper and lower grooves, and the contacting lines connecting the contact points themselves of both ball rolling grooves 3 and 5 intersect at right angles at the central position of the grooves.
On the other hand, the structures shown in FIG. 5 and FIG. 6 are of a two-point contact type, and in both of them, the groove surfaces of both opposed ball rolling grooves 3 and 5 and balls B are in contact at two points in each of the upper and lower grooves.
Traditionally, there has also been a structure in which the two-point contact and four-point contact are combined such as disclosed in Japanese Utility Model Laid-Open Application No. 64-53622. However, this disclosed structure is of a three-row type in which a four-point contact is arranged in the center while a two-point contact is provided each in the upper row and lower row to enable its contacting angles to be intersected, and the three-row structure makes the apparatus thick (that is, its height becomes great). There is further a structure disclosed in Japanese Patent Publication No. 3-31934, which requires space adjusting means 6 while the lower row is of a four-point contact type. As a result, when a load is applied to its slider, the both legs of the slider tend to be expanded, causing the four-point contact in the lower row to serve as if a two-point contact. Thus, the anticipated effect of the four-point contact is hard to be obtained.
A structure of such a type that the balls B are in contact at four points in all the ball rolling grooves in the upper and lower rows has the advantages in the aspect of vibration damping capacity, rigidity, load capacity, shock resistance, and others, but, on the other hand, a problem is encountered in that it lacks follow-up sensitivity when an extremely minute and precise operation is required.
Meanwhile, a structure of such a type that the balls B are in contact at two points in all the ball rolling grooves in the upper and lower rows is suited for the use of light-duty operations because the rolling frictions of the balls are small, but on the other hand, a problem is encountered in that it lacks the vibration damping capacity, rigidity, load capacity, shock resistance, and others.